Process for the production of alkali-earth-metal permanganates



Patented June 30, 1925.

UNITED i STATES PATENT OFFICE.

ROBERT E. WILSON, LEON W. PARSONS, AND STANLESIL. CHISHOLH, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNORS TO THE SECRETARY OF WAR OF THE UNITED STATES OF AMERICA, TRUSTEE.

PROCESS FOR THE PRODUCTION OF ALKALI-EARTH-HETAL PERMANGANATES.

No Drawing. Original application filed September 27, 1918, Serial No. 255,975. Divided and this applioation flled July 17, 1922. Serial .No. 575,759.

(GRANTED UNDER THE ACT OF MARCH 3, 1883; 22 STAT. L. 625.)

To all whom it may concern:

Be it known that we, ROBERT E. VVILsoN, LEON W. PARSONS, and STANLEY L. CHIs- HOLM, citizens of the United States, residing in Cambridge, Mass, have invented an Improvement in Processes for the Production of Alkali-Earth-Metal Permanganates, of which the following is a specification.

The invention described herein may be used by the Government, or any of its oilicers or employs in prosecution of Work for the Government, or by any other person in the United States, without payment of royalty thereon. ,r I

This application is a division of our copending application, Serial No. 255,975, filed .September 27, 1918, which has matured into Patent No. 1,453,562 of May 1, 1923.

The present invention relates to the production of alkali earth metal permanganates and especially the permanganates of calcium and magnesium as these have been found to be very eflicient. oxidizing agents for certain purposes, more efficient even than the permanganates of the alkali metals. This superiority is shown in the so-called British soda lime granules.

More specifically, the object of the invention is the development of a commercial process of producing the alkali earth metal permanganates, since so far as we are aware, their manufacture in quantity has never been attempted on a large scale or even on a small scale, except in German where they have been produced by a rat er expensive electrolytic process starting with potassium permanganate (KMnO,).

We have discovered that calcium or magnesium permanganate cannot be prepared directly by ordinary methods but that indirect methods must be used, e. g. by first forming a manganate, oxidizing this, and neutralizing the permanganic acid so formed with barium, calcium or magnesium hydroxide. y

We have investigated very thoroughly the possible methods" of qnaking calcium permanganate and believe that only four of them are at all workable. 'These are:

1. Preparatiomof silver permanganate by crystallization from slowly cooled solutions of silver nitrate and potassium or sodium permanganate. Calcium ermanganate is then formed metatheticall y by treatment with calcium chloride.

2. Selective transference and oxidation electrolysis of sodium or potassium manganate or permanganate and milk of lime or a calcium salt.

3. Electrolysis of ferromanganese anode into solution of a calcium salt.

4. Preparation of barium manganate by fusion or Wet methods, conversion to rmanganate by oxidation or acidification, metatheses into calcium permanganate b treatment with calcium sulphate or mil of lime.

Of these four possible methods; (1) is not a possible large scale method on account of its use of silver; (2) and (3) are electrolytic methods without a great deal of promise, and are to be considered elsewhere; (4) is the principal subject of this a plication.

Three distinct methods or preparing barium (or strontium) man anate have been here investigated. The rst of these methods involves heating together barium peroxide, hydroxide, or a salt, such as the nitrate or chlorate; with an oxide of manganese, as manganese dioxide in the presence of air or oxygen. Considerable work has been done upon fusions of this type, and beautiful green products were obtained, but the most favorable results obtained gave products containing only .810% BaMnO,,, the rest of the product consisting of residual MnO,, BaO and the BaMnO, from the thermal decomposition of the manganate. The thorough mixin of such dry sinterings is rather diflicult, ut quitenecessary; indeed even the fusions should be stirred to give the best results.

The second and more preferable of these methods involves the reaction of similar mixtures in a low melting fused medium such as fused sodium hydroxide, or sodium nitrate at temperatures well below a red heat. The cooled fused mass is extracted with water, the filtrate containing chiefly NaOH or NaNOQbeing evaporated to dryness, and

the fusion medium being returned to the process. The lnsoluble resldue consists of a baslo barlum mangam-manganate contalnmg tic to the process in the green ash (manganate) fusion. Barium manganate precipitates obtained on a small scale in this wet way contained 70-75% BaMnO the remainder appeared to consist of absorbed alkali, alkaline salts and barium carbonate, unless the green liquor had been previously boiled with milk of lime to remove the carbonate almost invariably present. Even in this case the precipitate generally contains some carbonate due to absorption of atmospheric carbon dioxide during manipulation of the alkaline barium mixtures. The use of the barium hydroxide would probably be preferable to that of a salt such as the chloride as no im urities are thus introduced into the caustic ltrate, to prevent its re-use in the green ash fusion. The preliminary removal of carbonate with Ca(OH) is preterable to using Ba(OH), for this purpose.

Such mixtures during treatment, should not be allowed to evaporate too far, as oxygen is then evolved, with the formation of a basic mangani-manganate similar to the product mentioned above in connection with the caustic fusions. Thus by evaporating to pasty-dryness, and thoroughly extracting with water, a dark blue green residue is obtained, in place of the smalt blue manganate, which contains only about 40% BaMnO,,.

To summarize, probably the best method of making BaMnO, is by preliminary fusion of NaOH and MnO which is leached, filtered and treated first with Ca(OH) 2 to precipitate CaCO and then with Ba(OH) to precipitate BaMnO,,. This gives a very igh purity BaMnO with a minimum amount of BaO used. Considering the great saving in the later conversion of this material to permanganate this method is undoubtedly the cheapest.

Barium manganate is an intermediate product in the manufacture of barium, calcium and magnesium permanganates. Barium manganate, as prepared by either fusion or precipitation methods ma be converted into barium permanganate either by direct oxidation, as by the use of chlorine or ozone, or by the action of acids, the liberated manganic acid acting as its own oxidizing agent, being itself partially reduced to manganese dioxide in consequence. The calcium permanganate may be obtained by metathesis with the somewhat soluble calcium sulphate, or by neutralizing the acid solution of permanganate with milk of lime.

Of these two methods, direct oxidation, on the one hand, and indirect oxidation, by acids on the other hand, the former appears to be at first sight preferable, because of its directness and because none of the product is used up in the process. Of the available oxidizing agents to oxidize directly manganate to permanganate including chlorine, bromine, and ozone, the first of these is the most practicable for technical use. Bromine is barred because of its scarcity and cost. The use of ozone is entirely too expensive. Even electrolytic oxidation methods, relatively much more eificient than the ozoning methods, involve much expensive apparatus.

Chlorination is undoubtedly the best and most economical process of converting BaMnO into Ba(MnOQ for any purpose where the large amount of chlorideimpurities could be tolerated. The nitric acid process is undoubtedly the next best, and it appears from the data now available that by careful removal of the nitrate formed by crystallization, a product pure enou 'h for certain more special uses may be ma e. If still greater purity is required recourse must be had to the carbonation or sulphation methods. Each has some advantages, but both have serious disadvantages for practical commercial operation. The final choice between the two would probably depend on local plant conditions. The Ca(MnO,) is made by either of two ways, depending on the process used in oxidizing the BaMnO,,. If Ba(MnOQ is made, the calcium salt is made by metathesis with CaSO filtering off the BaSO Owin to the much greater stability of Ba(Mn as compared with Ca(MnO all possible purification, filtration and concentration should be done before the final conversion to Ca(MnC) is made.

When a solution or a suspension of a manganate is acidified, manganic acid, being very unstable, breaks down into the relatively much more stable permanganic acid and manganese dioxide. Permanganic acid, while relatively much more stable than manganic acid, is, however, quite unstable except at low concentrations and low temperatures. Any plan of acid treatment involved in permanganate manufacture must take into account this instability. The action of light is similar but much less appreciable than that of heat.

Theaction of carbon dioxide, or of nitric and sulphuric acid respectively, may be regarded as that of typical acids as regards the reaction and the products obtained. Carbon dioxide is of course a. gas with very slight solubility in water, giving an acid Solution of exceedingly low hydrogen ion concentr'atiom-and in consequence drives the reaction to completion, mainly by removing insoluble equilibrium products.

This reaction is complete and irreversible on account of the insolubility of the products formed, but, as might be expected from the slight solubility of both the reacting substances, carbon dioxide and barium manganate, the solubility of the latter being comparable to barium sulphate, the rate of reaction is practically negligible at ordina temperatures and very slow even at the boiling temperature. The great advantage of carbonation for converting barium manganate lies in the very pure product to be obtained by this metho By using sulphuric acid in place of carbon dioxide, a soluble reacting substance is substituted for a very slightly soluble one and thus the rate of reaction is greatly increased at the corresponding temperatures. Two of the reaction products are as before insoluble. The use of this acid however, produces such a high hydrogen ion concentration that it is no longer possible to work above ordinary or room temperatures on account of the SPPltEIIlGOIlS decomposition of permanganic aci This decomposition is appreciable even at low temperatures.

This reaction is apparently also retarded by the insoluble product barium sulphate which seems to have a mechanical retarding effect upon the yet undissolved manganate, apparently by the formation of an insoluble coating upon the particles. This increases the amount of decomposition by increasing the length of treatment required for complete conversion and requires the use of excess H 80 In the CO process the reaction can be stopped when Ba(-MnO,) is

obtained according to the equation:

3BaMnO4+2CO:--)2BB.COa+Ba(MnO4)z+MnO1 By adding Ca(OI-I) to this reaction mixture, calcium permanganate is, obtained. This is essentially the equivalent of adding OaSO in the alternative method, except that the process is carried out in two stages, i. e., first the ste s of precipitating the BaSO, by the H 535, and then the neutralization of the HMnO, by means of Ca(OH) If milk of lime is employed for the neutralization the resulting filtered solution of calcium permanganate is of course contaminated with calcium sulphate.

In the case of nitric acid there is again one soluble reacting substance, in this resembling the action of sulphuric acid, but with an additional soluble product, this latter involving an impurity in the final prod not obtained. Upon the other hand the reaction proceeds so rapidly in the cold that decomposition is reduced to a minimum. As with sulphuric acid, however, at least some excess of nitric acid is required in order to work with the requisite rapidity due in this case to the fact that the reaction products are not as insoluble as before, and there is apparently a measurable equilibrium set up before the reaction is complete.

The nitric acid has absolutely no direct oxidizing action in this process, its action is solely that of an acid.

If barium hydroxide is used to neutralize the permanganic acid and any excess nitric acid, the resulting solution contains barium nitrate and permanganate, By evaporation it is possible to concentrate the relatively more stable barium permanganate and separate the less soluble barium nitrate. If calcium hydroxide is used for this neutralization and the clear filtrate concentrated by evaporation, the least soluble salt barium nitrate first tends to separate out, followed by calcium nitrate until when concentrated to about a 20% Ca'(MnO only about 5% (.la(NO,,) remains in solution and a much smaller proportion of Ba(NO As an example of our process the following experiment was carried out. '22 liters of green liquor made by leaching the mass from an ordinary NaOH-Mn0 fusion containing 5.5% of sodium manganate and 24.3% of caustic alkali, part of which was in the form of carbonate, was boiled for 5 hours with 4 kilograms of 90% hydrated lime to remove the carbonate. The sludge was removed by decantation and filtration and 12 liters of the filtrate containing 3.4c% of sodium manganate was boiled with 1 kilogram of hydrated barium hydroxide for one hour. The solution gradually became purplish but the green color of manganate still persisted and successive treatments with two portions of grams each of barium hydroxide for one hour each followed. The solution was cooled and filtered. The dried precipitate was a purplish blue color and contained about 1 kilogram of 74% barium manganate.

Fifty grams of the 74% barium manganate was suspended in one half liter of water and was treated with four successive portions of diluted nitric acid (1 to 10) each portion being slightly in excess of that theoretically required to produce complete conversion. The reacting mass was kept cool at all times. The final residue was entirely converted without requiring the boiling with sodium carbonate which it was necessary to employ to complete the conversion when carbonic or sulphuric acids were used. The mass was filtered and washed and the filtrate neutralized and concentrated to 20% barium permanganate, the crystals of nitrate being removed after cooling. Calcium sulphate was added to precipitate barium sulphate. The yield of calcium permanganate was 91.8% of the theoretical. The total time of treatment was four hours.

It is to be understood that by the term We claim as our invention: 1. In a process of making calcium permanganate, the steps which comprise neutralizingfermanganic acid.with an alkaline sulphate.

2. In a process of making alkali earth metal permanganates, the step which comprises treating barium permanganate with a salt of an alkali earth metal of lower atomic weight than barium and capable of precipitating an insoluble barium salt.

3. In a process of making alkali earth metal permanganates, the step which comprises treating barium permanganate with a sulphate of an alkali earth metal of lower atomic weight than barium.

4. In a process of making calcium permanganate, adding to barium manganate an excess of nitric acid, neutralizing the resulting solution with an alkaline compound of an alkali earth metal of greater atomic weight than calcium, concentrating and purifying the same and adding calcium sulphate to form barium sulphate and calcium permanganate.

ROBERT E. WILSON. LEON w. PARSONS. STANLEY L. CHISHOLM. 

